Couple anecdotal stories. Years ago we were bird hunting and my uncle yelled at me to get ready. A coyote emerged from the brush at around 15 yards. I hit him broadside 3 times with #8 quail loads and didn't even slow him down. A month or so later, a local farmer trapped him.......said his entire right side hide was full of bird shot.....life had probably been miserable for him.......but it didn't penetrate.....didn't kill him.
A few years before that......about 6th grade......kid in my class and his brother found their dad's 410. They were fooling around and big brother shot little brother in the head at pretty close range. It was a closed casket funeral.
My take? At close range of inside 10 feet, you hit somebody in the head with any kind of load coming out of a 12 gauge tube and chunks of his head are going to go flying. But as that distance increases, the effectiveness decreases. What was a mass of pellets is now a spread of pellets. What might have penetrated clothing doesn't.
I know a guy whose experience and judgement I respect......who claims to have a loaded shotgun in every room in his house......and they are loaded with #4 upland game loads.
I've shot several varmints......skunks and such......at a range of about 10 to 12 yard with #4 shot.......and it rolls them and renders them graveyard dead. That is some pretty tough hide...similar to clothing a human would be wearing........and it penetrates that and kills them. But compared to a human, vital area presents a smaller target and needed denser shot pattern to hit it.
So having said all that, I don't have close neighbors nor family to worry about, so for me my min would be #4 buck. That has killed a lot of coyotes and paper writing services online
writemypapers4me.net/essay-writing-service out to 30 yards or so and would do what a load of 7 1/2's would do and keep doing in from one end of the house to the other.
What I think is probably optimal is the same shell loaded with 7 1/2 birdshot, except replace the 7 1/2 low recoil payload with #0 buckshot. 1 oz payload of #0 buck is about 9 pellets cooking along at around 1300 fps. You would not want to be standing in front of that when it goes off.